Thrust bearing

ABSTRACT

In a thrust bearing supporting a load in a thrust direction in a rotary portion, a size of a curved surface in the forward side of a lubricating groove with respect to a relative rotating direction of an opposing sliding member is set to be larger than a size of a curved surface in the rearward side of the lubricating groove with respect to the relative rotating direction, and a depth of the lubricating groove is set to be deeper than a starting point in the side of a groove bottom of the curved surface formed in the groove shoulder in the forward side of the lubricating groove with respect to the rotating direction, so that a lubricating effect and a cooling effect are increased.

This is a nationalization of PCT/JP02/03001 filed Mar. 27, 2002 andpublished in Japanese.

TECHNICAL FIELD

The present invention relates to a thrust bearing which supports a loadin the thrust direction in a rotation portion.

BACKGROUND ART

A stator of a torque converter in an automatic transmission of a motorvehicle can rotate only in one direction by a one-way clutch, and athrust load applied to the stator is supported by a thrust bearing. Inthe thrust bearing of the torque converter, a low friction is requiredfor the purpose of reducing a loss of power energy transmission under ahigh speed driving condition so as to improve a specific fuelconsumption. Accordingly, as this kind of thrust bearing, there has beenemployed a needle bearing, or a copper washer or the like. However,since the needle bearing and the copper washer are expensive, needs fora synthetic resin thrust bearing which can be inexpensively manufacturedhave been increased in recent years.

FIGS. 14A and 14B show a synthetic resin thrust bearing in accordancewith a conventional art which is used in a torque converter or the like,in which FIG. 14A is a front view as seen from the side of a slidingsurface, and FIG. 14B is a partly enlarged cross sectional view cutalong a line XIV—XIV in FIG. 14A. As shown in the figures, in this kindof synthetic resin thrust bearing 100, a lot of lubricating grooves 102extending in the radial direction are formed on a sliding surface 101 ata predetermined interval in the circumferential direction. Each of thelubricating grooves 102 is provided so as to supply a lubricating oil tothe sliding surface 101, and groove shoulders 102 a and 102 b in bothsides are formed as curved surfaces or chamfer portions having the samesize.

However, in the conventional synthetic resin thrust bearing 100 shown inFIGS. 14A and 14B, since the lubricating oil introduced into thelubricating grooves 102 is hard to be sufficiently supplied to thelubricating surface 101, and further, since a depth d of the lubricatinggrooves 102 is shallow, a cooling effect achieved by the lubricating oilintroduced into the lubricating grooves 102 is not sufficient.Furthermore, because of the above insufficiency, there have been pointedout problems such that a friction with an opposing sliding member ishigh, a performance of the torque converter is lowered, and the specificfuel consumption is increased.

The present invention is made by taking the problems mentioned aboveinto consideration, and a technical object of the present invention isto provide a thrust bearing supporting a thrust load of a rotationportion, in which a friction with an opposing sliding member can besufficiently lowered even when the thrust bearing is made of a syntheticresin.

DISCLOSURE OF THE INVENTION

As a means for effectively achieving the technical object mentionedabove, in accordance with a first aspect of the present invention, thereis provided a thrust bearing comprising:

a lot of lubricating grooves formed on a sliding surface at apredetermined interval in the circumferential direction; and

curved surfaces formed in groove shoulders of each of the lubricatinggrooves,

wherein a size of the curved surface in the forward side of thelubricating groove with respect to a relative rotating direction of anopposing sliding member is set to be larger than a size of the curvedsurface, or the chamfer portion in place thereof, in the rearward sideof the lubricating groove with respect to the relative rotatingdirection.

In accordance with a second aspect of the present invention, there isprovided thrust bearing as recited in the first aspect, wherein a depthof the lubricating groove is set to be deeper than a starting point inthe side of a groove bottom of the curved surface formed in the grooveshoulder in the forward side of the lubricating groove with respect tothe rotating direction.

In accordance with a third aspect of- the present invention, there isprovided a thrust bearing as recited in the first aspect or the secondaspect, wherein a step portion for enlarging a groove width toward thecurved surface in the same side groove shoulder is formed in the forwardside of the lubricating groove with respect to the relative rotatingdirection of the opposing sliding member.

In accordance with a fourth aspect of the present invention, there isprovided a thrust bearing as recited in the first aspect or the secondaspect, wherein a groove inner wall in the forward side of thelubricating groove with respect to the relative rotating direction ofthe opposing sliding member is inclined such that the groove width isenlarged toward the curved surface in the same side groove shoulder.

In accordance with a fifth aspect of the present invention, there isprovided a thrust bearing as recited in any one of the first aspect tothe fourth aspect, wherein a depth of the groove bottom of thelubricating groove is made gradually shallower from an end portion inthe inner peripheral side toward an end portion in the outer peripheralside.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show a first embodiment of a thrust bearing inaccordance with the present invention, in which FIG. 1A is a front viewas seen from the side of a sliding surface, and FIG. 1B is a partlyenlarged cross sectional view cut along a line I—I in FIG. 1A;

FIG. 2 is a back view showing the first embodiment of the thrust bearingin accordance with the present invention;

FIG. 3 is a cross sectional view cut along a line III-O-III in FIG. 1A;

FIGS. 4A and 4B show an operation of a lubricating groove in accordancewith the present invention in comparison with an operation of thelubricating groove in accordance with the conventional art, in whichFIG. 4A is an explanatory view of the operation in accordance with thepresent invention, and FIG. 4B is an explanatory view of the operationin accordance with the conventional art;

FIG. 5 is a perspective view showing the operation of the lubricatinggroove in accordance with the present invention;

FIG. 6 is an explanatory chart showing a result obtained by measuring achange of friction coefficient by thrust loads to the thrust bearing inaccordance with the present invention and the thrust bearing inaccordance with the conventional art;

FIGS. 7A and 7B show a second embodiment of the thrust bearing inaccordance with the present invention, in which FIG. 7A is a front viewas seen from the side of a sliding surface, and FIG. 7B is a partlyenlarged cross sectional view cut along a line VII—VII in FIG. 7A;

FIGS. 8A and 8B show a third embodiment of the thrust bearing inaccordance with the present invention, in which FIG. 8A is a front viewas seen front the side of a sliding surface, and FIG. 8B is a partlyenlarged cross sectional view cut along a line VIII—VIII in FIG. 8A;

FIGS. 9A and 9B show a fourth embodiment of the thrust bearing inaccordance with the present invention, in which FIG. 9A is a front viewas seen from the side of a sliding surface, and FIG. 9B is a partlyenlarged cross sectional view cut along a line IX—IX in FIG. 9A;

FIGS. 10A and 10B show a fifth embodiment of the thrust bearing inaccordance with the present invention, in which FIG. 10A is a front viewas seen from a side of a sliding surface, and FIG. 10B is a partlyenlarged cross sectional view cut along a line X—X in FIG. 10A;

FIGS. 11A and 11B show a sixth embodiment of the thrust bearing inaccordance with the present invention, in which FIG. 11A is a front viewas seen from a side of a sliding surface. and FIG. 11B is a partlyenlarged cross sectional view cut along a line XI—XI in FIG. 11A;

FIG. 12 is a partly perspective view showing a seventh embodiment of thethrust bearing in accordance with the present invention;

FIG. 13 is a partly perspective view showing a eighth embodiment of thethrust bearing in accordance with the present invention; and

FIGS. 14A and 14B show a synthetic resin thrust bearing in accordancewith the conventional art, in which FIG. 14A is a front view as seenfrom the side of a sliding surface, and FIG. 14B is a partly enlargedcross sectional view cut along a line XIV—XIV in FIG. 14A.

BEST MODE FOR CARRYING OUT THE INVENTION

FIGS. 1A and 1B show a thrust bearing in accordance with a firstembodiment, in which FIG. 1A is a front view as seen from the side of asliding surface, and FIG. 1B is a partly enlarged cross sectional viewcut along a line I—I in FIG. 1A, FIG. 2 is a back view of the samethrust bearing, and FIG. 3 is a cross sectional view cut along a lineIII-O-III in FIG. 1A.

A thrust bearing 1 in accordance with the present embodiment is made ofa synthetic resin and formed in a flat annular shape, and is structuredsuch as to support a thrust load of a rotation member rotating only inone direction, for example, a stator of a torque converter in anautomatic transmission of a motor vehicle. The thrust bearing 1 isstructured such that one end surface in the axial direction forms asliding surface 2 with an opposing sliding member, and a lot oflubricating grooves 3 extending in the radial direction are formed onthe sliding surface 2 at a predetermined interval in the circumferentialdirection.

In each of the lubricating groove 3, a groove width W1 is set, forexample, about 1.4 mm, and curved surfaces 31 and 32 having differentsizes are formed in groove shoulders arranged in both sides of thelubricating groove 3. In particular, a relatively small first curvedsurface 31 is formed in the groove shoulder in the rearward side of thelubricating groove 3 with respect to a relative rotating direction S ofan opposing sliding member facing to the sliding surface 2, among thegroove shoulders in both sides of the lubricating groove 3, and a radiusR1 of curvature of the first curved surface 31 is set to be 0.5 mm orless. Further, a relatively large second curved surface 32 is formed inthe groove shoulder in the forward side of the lubricating groove 3 withrespect to the relative rotating direction S of the opposing slidingmember, and a radius R2 of curvature of the second curved surface 32 isset to be substantially larger than the radius R1 of curvature of thefirst curved surface 31. In the present embodiment, the radius R1 ofcurvature of the first curved surface 31 is formed, for example, about0.3 mm, and the radius R2 of curvature of the second curved surface 32is formed, for example, about 2 mm.

A depth d1 of a groove bottom 33 in each of the lubricating grooves 3 isformed deeper than a starting point 32 a in the side of the groovebottom 33 in the second-curved-surface 32. In the present embodiment, adepth d2 of the starting point 32 a with respect to the sliding surface2 is, for example, about 0.7 mm, and the depth d1 of the groove bottom33 is deeper than it and, for example, about 1.95 mm.

Further, an angle θ of a groove inner wall in the rearward side of thelubricating groove 3 with respect to the relative rotating direction Sof the opposing sliding member, that is, a groove inner wall 34 in theside of the first curved surface 31 forms an angle between 80 and 90degrees toward the opposite side to the rotating direction S, withrespect to the sliding surface 2, preferably forms an angle of 90degrees with respect to the sliding surface 2. Further, a width L in theperipheral direction of the sliding surface 2 is set to be, for example,about 6 mm in a center portion in the radial direction.

FIGS. 4A and 4B are explanatory views showing comparatively an operationof the lubricating groove 3 in accordance with the present embodimentand an operation of the lubricating groove in accordance with theconventional art, and FIG. 5 is a perspective view showing the operationof the lubricating groove 3 in accordance with the present embodiment.The thrust bearing 1 in accordance with the present embodiment isstructured, as shown in FIG. 4A, such that when the opposing slidingmember 4 facing to the sliding surface 2 of the thrust bearing 1 in thethrust direction relatively rotates in the direction of an arrow S, inother words, the counterclockwise direction in FIG. 1A, a lubricatingoil O introduced into the lubricating groove 3 runs over the slidingsurface 2 from the second curved surface 32 in the forward side of thelubricating groove 3 with respect to the rotating direction S in such amanner that the lubricating oil O is drawn in by the opposing slidingmember 4. Since the radius R2 of curvature and the depth of the startingpoint 32 a of the second curved surface 32 is larger than the radius R1of curvature of the first curved surface 31, the lubricating oil O tendsto interpose into a sliding gap δ between the sliding surface 2 and theopposing sliding member 4 from the lubricating groove 3, andconsequently, a wedge effect of the lubricating oil O is increased inaccordance with the structure that the gap is reduced with respect tothe relative rotating direction S of the opposing sliding member 4,whereby an effective bearing pressure P is generated.

On the other hand, since the first curved surface 31 in the oppositeside to the second curved surface 32 is structured such as to enlargethe gap with respect to the relative rotating direction S of theopposing sliding member 4, a reverse wedge effect of drawing out alubricating oil film from the sliding gap δ between the sliding surface2 and the opposing sliding member 4 is generated in correspondence tothe sliding motion of the opposing sliding member 4. However, since theradius R1 of curvature of the first curved surface 31 is substantiallysmall in comparison with the radius, R2 of curvature of the secondcurved surface 32, the reverse wedge effect achieved by the first curvedsurface 31 is small in comparison with the wedge effect achieved by thesecond curved surface 32. In particular, when the radius R1 of curvatureof the first curved surface 31 is set to be 0.5 mm or less, the reverewedge effect is hardly generated.

Further, when the angle θ of the groove inner wall 34 in the side of thefirst curved surface 31 is small, the reverse wedge effect is generatedthereby. However, since the angle θ is approximately 90 degrees. in thepresent embodiment, the reverse wedge effect caused by the groove innerwall 34 is hardly generated.

On the contrary, in the thrust bearing 100 in accordance with theconventional art shown in FIG. 4B, a groove shoulder 102 b causinggeneration of the bearing pressure P on the basis of the wedge effect inthe forward side of a lubricating groove 102 with respect to therotating direction S, and a groove shoulder 102 a causing generation ofthe reverse wedge effect in the rearward side of the lubricating groove102 are formed so as to have the same radius of curvature with eachother. Accordingly, the wedge effect achieved by the curved surface 102b is cancelled by the reverse wedge effect achieved by the curvedsurface 102 a, so that the bearing pressure P can not be enlarged.

Thus, on the basis of the thrust bearing 1 in accordance with thepresent embodiment, it is possible to obtain a remarkable bearingpressure P for expanding the sliding gap δ. Accordingly, even when thethrust bearing 1 is made of the synthetic resin, a friction between theopposing sliding member 4 and the sliding surface 2 is reduced, and itis possible to effectively reduce a loss of power energy. Further, it istherefore possible to improve a performance of the torque converter andit is possible to improve the specific fuel consumption.

Further, in the thrust bearing 100 in accordance with the conventionalart shown in FIG. 4B, since a groove bottom 102 c is continuous from thecurved surfaces of the groove shoulders 102 a and 102 b, a groove depthd0 is shallow and is about 0.5 mm, so that the lubricating oil is lessflown within the lubricating groove 102.

On the other hand, in the present embodiment, the depth d1 of the groovebottom 33 in the lubricating groove 3 is deeper than the starting point32 a in the side of the groove bottom 33 in the second curved surface32, and the angle θ of the groove inner wall 34 in the rearward side ofthe lubricating groove 3 with respect to the rotating direction S formsthe angle between 80 and 90 degrees toward the opposite side to therotating direction S with respect to the sliding surface 2. Accordingly,a negative pressure portion n is generated near the groove inner wall 34within the lubricating groove 3. Further, as described above, since thereverse wedge effect of drawing out the lubricating oil film from thesliding gap δ is small in the first curved surface 31, the lubricatingoil O is supplied to the negative pressure portion n not from thesliding gap δ but from both ends 3 a and 3 b in the radial direction ofthe lubricating groove 3 in major part, as shown in FIG. 5. Inparticular, since a centrifugal force is applied to the lubricating oil,the lubricating oil is introduced into the lubricating groove 3 mainlyfrom the inner peripheral side of the thrust bearing 1 (the end portion3 a of the lubricating groove 3).

Therefore, since the lubricating oil can be actively flown between theinner and outer peripheries of the thrust bearing 1 and the lubricatinggroove 3, it is possible to increase a cooling effect of the slidingportion. Further, since the thick lubricating oil film is kept in thesliding gap 6 as the result, it is possible to reduce a friction betweenthe opposing sliding member 4 and the sliding surface 2.

FIG. 6 shows a result obtained by measuring a change of frictioncoefficient caused by thrust loads in the thrust bearing in accordancewith the present embodiment and the thrust bearing in accordance withthe conventional art. On the basis of the test result, it is confirmedthat the thrust bearing in accordance with the present embodiment isindicative of a low friction and stable bearing performance, while thethrust bearing in accordance with the conventional art is indicative ofa rapid increase of the friction coefficient even under the small thrustloads. Further, it is known that the thrust bearing in accordance withthe present embodiment maintains a comparatively low frictioncoefficient owing to a sufficient cooling effect of the lubricating oil,even in the case that the thrust bearing is reverse rotated, that is,the relative rotating direction of the opposing sliding member is set tothe opposite direction to the arrow S in FIG. 4B.

FIGS. 7A and 7B show a thrust bearing in accordance with a secondembodiment, in which FIG. 7A is a front view as seen from the side of asliding surface, and FIG. 7B is a partly enlarged cross sectional viewcut along a line VII—VII in FIG. 7A. The thrust bearing 1 in accordancewith this embodiment is employed in a structure in which the opposingsliding member relatively rotates in the reverse direction to that inFIGS. 1A and 1B, that is, in a clockwise direction in FIG. 7A. A crosssectional shape of each of the lubricating grooves 3 is formed in asymmetrical cross sectional shape to that of FIG. 1B described above,with respect to a circumferential direction. Accordingly, the sameoperation and effect as those of the first embodiment can be achieved.

FIGS. 8A and 8B show a thrust bearing in accordance with a thirdembodiment of the present invention in which FIG. 8A is a front view asseen from the side of a sliding surface. and FIG. 8B is a partlyenlarged cross sectional view cut along a line VIII—VIII in FIG. 8A. Thepresent embodiment is structured such that an angled surface 36 having adepth d2 from starting print 36 a is formed in the forward side withrespect to the relative rotating direction S of the opposing slidingmember. Further, an opposed angled surface 35 is formed in the grooveshoulder in the rearward side with respect to the relative rotatingdirection S of the opposing sliding member.

FIGS. 9A and 9B show a thrust bearing in accordance with a fourthembodiment of the present invention, in which FIG. 9A is a front view asseen from the side of a sliding surface, and FIG. 9B is a partlyenlarged cross sectional view cut along a line IX—IX in FIG. 9A. Thepresent embodiment is structured such that a step portion 37 having adepth d3 is formed in the forward side with respect to the relativerotating direction S of the opposing sliding member. Further, in thesame manner as that in FIGS. 1A and 1B, the first curved surface 31having the radius R1 of curvature of 0.5 mm or less is formed in thegroove shoulder in the rearward side with respect to the relativerotating direction S of the opposing sliding member, and the secondcurved surface 32 having the radius R2 of curvature which issubstantially larger than the radius R1 is formed in the groove shoulderin the forward side. Further, a groove width W2 between the groove innerwall 34 and the step portion 37 is set to be about a half of a groovewidth W1 between the groove inner wall 34 and the rising portion of thestep portion 37.

Therefore, in accordance with the present embodiment, since thelubricating oil introduced into the lubricating groove 3 is introducedinto the sliding surface 2 from the second curved surface 32 via thestep portion 37, the lubricating oil is further easily interposed in thesliding gap, and an improved bearing effect can be obtained. In thiscase, the step portion 37 may be formed, in the same manner, in thestructure in which a chamfer portion is formed in place of the firstcurved surface 31.

FIGS. 10A and 10B show a thrust bearing in accordance with a fifthembodiment of the present invention, in which FIG. 10A is a front viewas seen from the side of a sliding surface, and FIG. 10B is a partlyenlarged cross sectional view cut along a line X—X in FIG. 10A. Thepresent embodiment is structured such that a chamfer portion 37 a isformed in a shoulder portion of the step portion 37 in accordance withthe fourth embodiment shown in FIGS. 9A and 9B mentioned above. Theother structures are the same as those in FIGS. 9A and 9B. Accordingly,in the same manner as the embodiment shown in FIGS. 9A and 9B, thelubricating oil well runs over the step portion 37 from the side of thegroove bottom 33, so that an improved bearing effect can be obtained.

In this case, in FIGS. 9A, 9B, 10A and 10B, only one step portion 37 isformed, however, plural stages of step portions having different depthsmay be formed in such a manner as to be made shallower step by steptoward the second curved surface 32.

FIGS. 11A and 11B show a thrust bearing in accordance with a sixthembodiment of the present invention, in which FIG. 11A is a front viewas seen from the side of a sliding surface, and FIG. 11B is a partlyenlarged cross sectional view cut along a line XI—XI in FIG. 11A. Thepresent embodiment is structured such thaf a groove inner wall in theforward side with respect to the relative rotating direction S of theopposing sliding member, that is, a groove inner wall 38 in the side ofthe second curved surface 32 is inclined at an angle θ1. Further, agroove width W3 of the groove bottom 33 is set to be about a half of thegroove width W1 between the groove inner wall 34 and a starting point 32a in the side of the groove bottom 33 of the second curved surface 32.The other structures are the same as those in FIGS. 1A and 1B.

In accordance with the present embodiment, the sliding surface 2 of thethrust bearing 1 and the opposing sliding member facing to the slidingsurface 2 in the thrust direction relatively rotate in the direction ofthe arrow S. Accordingly, the lubricating oil introduced into thelubricating groove 3 is introduced onto the sliding surface 2 from thesecond curved surface 32 in the forward side of the lubricating groove 3with respect to the rotating direction S in such a manner that thelubricating oil is drawn in by the opposing sliding member, and thelubricating oil runs over the side of the second curved surface 32 fromthe groove bottom 33 so as to supplement it. In this structure, the flowof the lubricating oil becomes smoother than the case that the grooveinner wall 38 is vertical to the sliding surface 2. Therefore, thelubricating oil is further easily interposed in the sliding gap, and animproved bearing effect can be obtained. In this case, the inclinedgroove inner wall 38 may be applied, in the same manner, to thestructure in which the chamfer portion as shown in FIGS. 9A and 9B isformed in place of the first curved surface 31. the inclined grooveinner wall 38 may be applied, in the same manner, to the structure inwhich the first chamfer portion 35 and the second chamfer portion 36 asshown in FIGS. 9A and 9B are formed.

FIG. 12 is a partly perspective view showing a thrust bearing inaccordance with a seventh embodiment of the present invention. In thepresent embodiment, the groove bottom 33 of each of the lubricatinggrooves 3 is formed so as to be made shallower gradually from the endportion 3 a in the inner peripheral side of the thrust bearing 1 towardthe end portion 3 b in the outer peripheral side. A cross sectionalshape of a center portion in a longitudinal direction of each of thelubricating grooves 3 is the same as that in FIG. 1B described above,that is, the first curved surface 31 having the radius of curvature of0.5 mm or less is formed in the groove shoulder in the rearward side ofthe lubricating groove 3 with respect to the relative rotating directionS of the opposing sliding member facing to the sliding surface 2, andthe second curved surface 32 having the radius of curvature which issubstantially larger than that of the first curved surface 31 is formedin the groove shoulder in the forward side. Further, the depth d1 of thegroove bottom 33 is deeper than the depth of the starting point 32 a inthe side of the groove bottom 33 in the second curved surface 32, at theend portion 3 a in the inner peripheral side of the thrust bearing 1,and is similar to the depth d2 at the end portion 3 b in the outerperipheral side. The other structures are the same as that in FIGS. 1Aand 1B.

The opposing sliding member relatively rotates in the direction of thearrow S, whereby the centrifugal force is applied to the lubricating oilO existing on the periphery thereof. Accordingly, the lubricating oil Ois introduced into the lubricating groove 3 from the inner peripheralside of the thrust bearing 1, that is, from the end portion 3 a. At thistime, in accordance with the embodiment shown in FIGS. 9A and 9B, sincethe groove bottom 33 becomes shallower in accordance with the movementof the lubricating oil O toward the outer peripheral side of the thrustbearing 1 within the lubricating groove 3, the lubricating oil O isefficiently introduced onto the sliding surface 2 from the second curvedsurface 32. Further, since the diminishing passage in which the crosssectional area is reduced gradually toward the outer peripheral side isformed between the lubricating groove 3 and the opposing sliding member,the lubricating oil O is pressurized in the process of moving toward theouter peripheral side of the thrust bearing 1 within the passage (thelubricating groove 3) on the basis of the centrifugal force.Accordingly, the bearing pressure is increased and an improved bearingeffect can be obtained.

FIG. 13 is a partly perspective view showing a thrust bearing inaccordance with an eighth embodiment of the present invention. Thepresent embodiment corresponds to a structure in which the structure inFIG. 12 is applied to the embodiment shown in FIG. 9A and 9B mentionedabove. In the present embodiment, the depth d1 of the groove bottom 33is deeper than the step portion 37 at the end portion 3 a at the innerperipheral side of the thrust bearing 1, and is similar to the depth ofthe step portion 37 at the end portion 3 b in the outer peripheral side.Accordingly, in the same manner as that in FIG. 12, the groove bottom 33is made shallower in accordance with the movement of the lubricating oilO toward the outer peripheral side of the thrust bearing 1 within thelubricating groove 3. Thus, the lubricating oil O is efficientlyintroduced onto the sliding surface 2 from the step portion 37 via thesecond curved surface 32, and is pressurized. Therefore, the bearingpressure is increased, and an improved bearing effect can be obtained.

Further, in each of the embodiments shown in FIGS. 10A, 10B, 11A and11B, the structure may be made, in the same manner, such that the groovebottom 33 is made shallower gradually from the end portion in the innerperipheral side of the thrust bearing 1 toward the end portion in theouter peripheral side, whereby it is possible to further improve thebearing effect.

Further, in each of the embodiments in FIGS. 9A and 9B to FIG. 13, eachof the lubricating grooves 3 may be formed in a symmetrical crosssectional shape with the illustrated shape, in correspondence to therelative sliding direction of the opposing sliding member.

In this case, the thrust bearing 1 in accordance with the presentinvention is not limited to the bearing means of the stator of thetorque converter in the automatic transmission of the motor vehicle, andis useful for a thrust bearing of the other rotary equipment.

INDUSTRIAL APPLICABILITY

As described above, in accordance with the thrust bearing on the basisof the first aspect of the present invention, the curved surface whichis larger than the size of the curved surface or the chamfer portion inthe rearward side of the lubricating groove is formed in the grooveshoulder in the forward side of the lubricating groove with respect tothe relative rotating direction of the opposing sliding member. Thus, inthe forward side of or the chamfer portion the lubricating groove, thelubricating oil tends to interpose into the sliding gap between thesliding surface and the opposing sliding member and the wedge effect ofthe lubricating oil is enlarged, and in the rearward side of thelubricating groove, the reverse wedge effect becomes significantlysmall. Therefore, it is possible to sufficiently reduce the frictionwith the opposing sliding member even in the case that the thrustbearing is made of the synthetic resin, and it is possible to provide athrust bearing which is inexpensive and has an excellent bearingperformance.

In accordance with the thrust bearing on the basis of the second aspectof the present invention, the depth of the lubricating groove is set tobe deeper than the starting point in the side of the groove bottom ofthe curved surface or the chamfer portion formed in the groove shoulderin the forward side of the lubricating groove with respect to therotating direction. Accordingly, the major part of the lubricating oilis supplied to the lubricating groove from both ends in the radialdirection of the lubricating groove, and the lubricating oil is activelyflown between the inner and outer peripheries of the thrust bearing andthe lubricating groove, so that the cooling effect of the lubricatingportion can be increased. Therefore, in this case, it is possible toachieve the reduction of friction by the thick lubricating film.

In accordance with the thrust bearing on the basis of the third aspectof the present invention, the step portion is formed in the forward sideof the lubricating groove with respect to the relative rotatingdirection, of the opposing sliding member. Accordingly, it is possibleto further increase the effects obtained by the first aspect or thesecond aspect of the present invention.

In accordance with the thrust bearing on the basis of the fourth aspectof the present invention, the groove inner wall in the forward side ofthe lubricating groove with respect to the relative rotating directionof the opposing sliding member is inclined. Accordingly, it is possibleto further increase the effects obtained by the first aspect or thesecond aspect of the present invention.

In accordance with the thrust bearing on the basis of the fifth aspectof the present invention, the depth of the groove bottom of thelubricating groove is made shallower gradually from the end portion inthe inner peripheral side toward the end portion in the outer peripheralside. Accordingly, the lubricating oil can be efficiently interposedinto the sliding gap between the sliding surface and the opposingsliding member, and the lubricating oil moving to the outer peripheralside within the groove is pressurized by the centrifugal force, wherebythe bearing pressure is increased. Therefore, it is possible to furtherincrease the effects obtained by the first aspect to the fourth aspectof the present invention.

1. A thrust bearing comprising: a plurality of lubricating groovesformed on a sliding surface at a predetermined interval in acircumferential direction; curved surfaces formed in groove shoulders ofeach of the lubricating grooves, a size of the curved surface in aforward side of said lubricating groove with respect to a relativerotating direction of an opposing sliding member being set to be largerthan a size of the curved surface or a chamfer portion in a rearwardside of said lubricating groove with respect to said relative rotatingdirection; and a step portion for enlarging a groove width toward thecurved surface in a same side groove shoulder being formed in theforward side of the lubricating groove with respect to the relativerotating direction of the opposing sliding member.
 2. A thrust bearingcomprising: a plurality of lubricating grooves formed on a slidingsurface at a predetermined interval in a circumferential direction;curved surfaces formed in groove shoulders of each of the lubricatinggrooves, a size of the curved surface in a forward side of saidlubricating groove with respect to a relative rotating direction of anopposing sliding member being set to be larger than a size of the curvedsurface or a chamfer portion in a rearward side of said lubricatinggroove with respect to said relative rotating direction; and a grooveinner wall in the forward side of the lubricating groove with respect tothe relative rotating direction of the opposing sliding member beinginclined such that a groove width is enlarged toward the curved surfacein a same side groove shoulder.